TRANSACTIONS OF SECTION B. 839 



titrating it with standard permanganate solution in the presence of a sufficient 

 amount of magnesium sulphate. As a result of four experiments, the average sum 

 of the magnesium equivalents of the cuprous oxide, the copper, and the hydrogen 

 amounted to 0'102 gram, and the average weight of magnesium used was O'lOS 

 gram. The ratios of the weights of hydrogen, copper, and cuprous oxide produced 

 Vfere constant only when the conditions of the experiment were precisely similar. 



AVhen the hot cupric sulphate is dilute, or when it is employed at ordinary 

 temperature, the reaction pursues at first a similar course, hut it soon becomes 

 very considerably delayed by the formation of a green basic cupric salt, inter- 

 mingled with colourless basic magnesium salt. Thus, the reaction on the magnesium 

 was usually complete in ten minutes in an excess of a hot, strong solution of cupric 

 sulphate ; but in weak and cold solutions it often extended over several days, and 

 even a week. 



The percentage of hydrogen, compared with that which is equivalent to the 

 magnesium employed, was in the case of the hot solution 34'7 ; with the cold solu- 

 tion, it was 41-6 with weak solution, and 30'6 with saturated solution. 



Various explanations have been given of the causes which lead to deposition of 

 cuprous oxide and to evolution of hydrogen. It has been suggested that the 

 change is due to impurity in the copper salt ; this we have disproved by using a 

 salt purified by frequent recrystallisation, and yielding :.'5-23 per cent, of copper 

 (theory = 25"39) ; we have also proved the purity of the magnesium employed. 

 Divers suggests that the evolution of hydrogen is due to the action of the mag- 

 nesium upon free sulphuric acid, which has been formed by hydrolysis of the 

 cupric salt. This seems to us to be an insufficient explanation of the rapidity 

 with which hydrogen is evolved. Cold cupric sulphate solution was found to give 

 no acid reaction with methyl-orange, although it is faintly acid to litmus paper. 

 Yet such a solution gives an immediate evolution of hydrogen when magnesium is 

 immersed in it, the evolution of the gas being very rapid in a hot and strong solu- 

 tion. After carefully studying the change, we are inclined to attribute the evolu- 

 tion of hydrogen in small degree to the presence of free sulphuric acid formed by 

 hydrolysis in cold solution, and in greater degree to the same cause in hot solution. 

 This involves the formation and separation of basic salt. This reaction, however, 

 does not account for all the hydrogen evolved, and one of us will be prepared 

 before long to advance a further explanation to account for this. Divers further 

 suggests that cuprous sulphate is formed and almost immediately converted by the 

 action of the basic cupric salt into cuprous oxide ; this theory we also find to be 

 untenable. 



The immediate separation of cuprous oxide and evolution of hydrogen, without 

 formation of basic salt, which occurs at the commencement of the reaction, may be 

 represented by the equation : 



2Mg + 20uS0, + H.O = 2MgS0, + Cu^O + H,. 



The action of the magnesium-zinc couple has been proved to be too alow to explain 

 the rapid escape of hydrogen, and if this were the origin of the hydrogen, its escape 

 would not immediately follow the immersion of the magnesium. 



9. A Note on Alkaline Chlorates and Sidphates of Heavy Metals. 

 By W. R. HoDGKiNSON and A. H. Coote. 



Many solid sulphates, whether containing water of crystallisation or anhydi'ous, 

 when mixed and gently heated with potassium or sodium chlorate give off 

 chlorine gas in addition to oxygen. In many cases the evolution of the chlorine 

 seems to precede that of the oxygen. With sulphates containing crystallisation 

 water chlorine is evolved vdth it, as steam, on heating. Mixtures also of anhy- 

 drous sulphates, as those of copper and manganese with chlorates, give off a 

 mixture of oxygen and chlorine at temperatures very little above 100° C. 



